compat: check arch_prctl() return code for ARCH_MAP_VDSO_32

On first versions of x86 compat patches it returned 0 or err.
In merged version it returns error < 0 or vDSO blob's size.

travis-ci: success for Rectify 32-bit compatible C/R on x86
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

criu/include/parasite-vdso.h

@@ -80,7 +80,7 @@ static inline bool is_vdso_mark(void *addr)
 }
 
 extern int vdso_do_park(struct vdso_symtable *sym_rt, unsigned long park_at, unsigned long park_size);
-extern int vdso_map_compat(unsigned long map_at, unsigned long park_size,
+extern int vdso_map_compat(unsigned long map_at, unsigned long *park_size,
 		struct vdso_symtable *sym_rt);
 extern int vdso_proxify(char *who, struct vdso_symtable *sym_rt,
 			unsigned long vdso_rt_parked_at, size_t index,

criu/pie/parasite-vdso.c

@@ -75,7 +75,7 @@ int vdso_do_park(struct vdso_symtable *sym_rt, unsigned long park_at, unsigned l
 extern int vdso_fill_symtable_compat(uintptr_t mem, size_t size,
 		struct vdso_symtable *t);
 
-int vdso_map_compat(unsigned long map_at, unsigned long park_size,
+int vdso_map_compat(unsigned long map_at, unsigned long *park_size,
 		struct vdso_symtable *sym_rt)
 {
 	unsigned long search_vdso;
@@ -84,18 +84,22 @@ int vdso_map_compat(unsigned long map_at, unsigned long park_size,
 	pr_debug("Mapping compatible vDSO at %lx\n", map_at);
 
 	ret = sys_arch_prctl(ARCH_MAP_VDSO_32, map_at);
-	if (ret)
+	if (ret < 0)
 		return ret;
+	*park_size = (unsigned long)ret;
 
 	/*
 	 * We could map VVAR firstly, or VDSO.
 	 * Try to find VDSO pages in this couple of parking pages.
+	 * XXX: Please, FIXME - compat vdso/vvar sizes should be counted
+	 * at CRIU start time by parsing /proc/<...>/maps then by searching
+	 * ELF magic.
 	 */
-	for (search_vdso = map_at; search_vdso < map_at + park_size;
+	for (search_vdso = map_at; search_vdso < map_at + *park_size;
 			search_vdso += PAGE_SIZE)
 	{
 		ret = vdso_fill_symtable_compat(search_vdso,
-			map_at + park_size - search_vdso, sym_rt);
+			map_at + *park_size - search_vdso, sym_rt);
 		if (!ret)
 			return 0;
 	}
@@ -113,9 +117,11 @@ int __vdso_fill_symtable(uintptr_t mem, size_t size,
 }
 #else
 int vdso_map_compat(unsigned long __always_unused map_at,
-		unsigned long __always_unused park_size,
+		unsigned long __always_unused *park_size,
 		struct vdso_symtable __always_unused *sym_rt)
 {
+	/* shouldn't be called on !CONFIG_COMPAT */
+	BUG();
 	return 0;
 }
 int __vdso_fill_symtable(uintptr_t mem, size_t size,

criu/pie/restorer.c

@@ -1125,7 +1125,7 @@ long __export_restore_task(struct task_restore_args *args)
 	if (args->compatible_mode) {
 		/* Map compatible vdso */
 		if (vdso_map_compat(args->vdso_rt_parked_at,
-				vdso_rt_size, &args->vdso_sym_rt))
+				&vdso_rt_size, &args->vdso_sym_rt))
 			goto core_restore_end;
 	}